Many useful dental instruments employ substantial vibratory motion at a tool tip of the instrument for cleaning, scaling and like operations. The tool tips are designed to produce flexural and longitudinal vibrations with flexural motions of from about 0.02 to 0.2 mm. The tip is typically attached to an electro-mechanical part or section that can be induced to vibrate at high frequency. The instrument is driven by an electronic generator at relatively high frequencies, typically on the order of above 20 kHz, to obtain adequate motion and to minimize objectionable noise since the human hearing threshold is about 18 kHz. The energy generator and related electro-mechanical section may be any one of several types such as electro-dynamic, piezo electric, or magnetostrictive. Design of the tip and its related electro-mechanical components involves combining a number of parameters to produce mechanical resonances (harmonic vibrations) at the driving frequency to produce amplified mechanical motion, particularly at the distal tip end.
In many operations employing a vibrating tip tool, it is useful and often necessary to have a source of water or other fluid impinging upon the workpiece surfaces and/or tool surfaces in order to cool them or remove debris generated by the work. For example, in dental applications, when an ultrasonically vibrated tip contacts a tooth surface, as required for performing a cleaning operation, the moving tip against the tooth surface produces heat. The patient may experience a pain sensation which can be severe if the operator applies even mild pressure against the tooth while cleaning. Water or some other fluid is usually supplied to the tooth surface in order to remove the heat and minimize pain and possible heat damage to the tooth. In addition, a number of the electro-mechanical devices utilized in providing a vibrating tip generate heat internally during operation.
An example of an ultrasonic dental tool, wherein a handpiece containing a coil applies an electro-magnetic field to a magnetostrictive insert body to which a tool tip is fixed is described by Perdreaux in U.S. Pat. No. Re. 30,536 (CAVITRON®). In the Perdreaux design, heat caused by electrical and mechanical friction losses within the tool during vibration are dissipated by means of a cooling fluid that flows axially with respect to the tool insert, over the active magnetostrictive element or stack, emerging from an annular space between the insert and the handpiece and being directed toward the working end of the tool. The CAVITRON® arrangement is such that heat generated by the insert body warms the fluid which is then directed, as a convenient source of irrigating, flushing and/or cooling fluid, onto the active tip or workpiece area. The warm fluid minimizes reactions by patients who have sensitivity to cold temperatures.
In a number of dental operations, the vibrating tip is guided over and about tooth surfaces by the operator. The tip must be capable of penetrating between teeth and under or below the gingiva or gum line. Generally, the tip must be small in cross-section, ideally having a pointed tip with a tapered cross-section extending about 2.5 to 5 mm back from the distal tip end to allow adequate access between teeth and gingiva.
In addition, the tip is universally curved or shaped to conform to or be compatible with tooth surfaces. Useful tips will curve sufficiently to permit spanning the tooth frontal surface when entrance to abutting surfaces is needed or when access to subgingival zones about the oral cavity are required.
Experience in using such ultrasonically activated and irrigated tips has demonstrated that a combination of tip shape and fluid delivery system must be selected such that the tip is strong enough to support vibrating motion stresses at useable amplitudes. The forming process must be such that minute fractures or other weak points are not introduced into the tip material that might become focal points of breakage during use.
A number of vibrating tools, generally similar to the Perdreaux tool, as described above, are now in dental, medical, veterinary and other uses. These tools employ various designs for directing water or another fluid adjacent to or onto the surfaces being worked upon, as a means of cooling workpiece surfaces and removing debris from the work area. (The term “water” may be used interchangeably in this disclosure herein with “fluid” without intending to imply a limitation by selecting one or the other.) For example, a number of ultrasonically activated tools employ separate fluid conduits, external to the instrument itself, for conducting water and other fluids adjacent the tip or onto the workpiece or tip. Kleesattel et al in U.S. Pat. No. 3,076,904 employ a capillary, run externally to the handpiece, with a nozzle formed of a bendable metal extending very near the tip for directing water onto the dental surfaces being worked upon. A difficulty with such arrangements is that the capillary may obstruct free use of the tool tip.
A number of ultrasonic tool tips include internal fluid passageways bored along the longitudinal center axis of the tip component or body. In many such tips, a fluid discharge orifice is formed at the distal end of the tool, for directing fluid onto the workpiece. Such tip design is described, for example, by Balamuth et al in U.S. Pat. No. 3,924,335 for a piezo electric crystal vibrated dental tool. A difficulty in employing this tip design is that the tip must generally be of a relatively large diameter, on the order of greater than 1 mm, in order to have a sufficiently strong tip and a passageway that provides an adequate flow of fluid. Such a tip may be too blunt for many dental uses as it does not allow adequate tapering such that the tool thus cannot penetrate small inter-tooth spaces and can damage gums when used subgingivally.
Many tips having internal central axial passageways that include a fluid discharge orifice formed by removing a longitudinal lateral portion of the cylindrical wall of the tip as the distal tip end is approached, as shown in Haydu U.S. Pat. No. 3,488,851 and Richman U.S. Pat. No. 3,589,012, for example. In Banko U.S. Pat. No. 3,930,173, Robinson U.S. Pat. No. 3,703,037 and Warrin U.S. Pat. No. 5,125,837, the tip is cut away such that remaining lateral walls of the distal tip from a channel for helping direct water discharging from the center axis bore onto the workpiece. A transducer activated tool tip having a water channel is shown in U.S. Pat. No. 5,567,153, which is hereby incorporated by reference for such disclosure.
All of the tips that discharge fluid from the distal end of the tip or close thereto are discharging from a tip at or before a point of high flexural motion, which motion often causes the fluid at this point to spray or form a mist adjacent to the tip and workpiece. Such spraying and misting may prevent fluid from reaching the workpiece area and, instead, dispense it over a relatively wide area, including onto the patient and operator.
Conventional dental ultrasonic scaling procedures often involve placement of an ultrasonic scaler tip into a small area such as a periodontal pocket. It is desired to make the working end of the tool such as the tip of the tool as thin as possible so that the user can observe the target area. (By tip it is understood to mean any portion of the working surface of tool itself, and may include single or monolithic structures or various connected parts that may even be removable, all of which are within the scope of the present disclosure.) However, reducing the outside diameter of the tool without reducing the diameter of a fluid passage therein, results in a thinner tip wall and an increased possibility of tool breakage during use. Ultrasonic tools such as dental scaling tools having a working end often are fabricated by starting with an unbent blank. In some cases, a back bend is put into one end of the blank (see for example, U.S. Pat. No. 6,494,714 which is hereby incorporated by reference for such disclosure) and the fluid hole is added to the blank by some means such as drilling, electro-discharge machining (EDM) or other conventional technique.
For example, in the FSI-SLI-10S dental scaler tip available from DENTSPLY International of York, Pa., the fluid hole diameter is 0.014 inches and axially transverses the majority of the working end or tip end length of the tool. After the hole is placed into the bent blank, the blank is bent into its final shape. While this device provides for an excellent and effective dental tool, when the fluid hole is bent during the final shaping of the tool, the once-circular (or other shaped) hole is deformed, such as to a more oval shape. The deformed hole has a higher probability of capturing particles inherent in the water supply system that normally passes through the fluid hole, leading to an increased possibility of becoming clogged. The dental tool described herein overcomes the deficiencies of the prior art.